Neonatal hyperbilirubinemia at sub-kernicteric levels has been shown to have lasting neurological effects, thought to be related to the neurotoxicity of unconjugated bilirubin. The overall objective of this proposed research is to elucidate the molecular basis of bilirubin neurotoxicity in the expectation that the understanding of this phenonmenon will lead to new and/or improved treatment of neonatal hyperbilirubinemia. The molecular and electronic structure of bilirubin will be studied by x-ray crystallography and molecular orbital theory for any characteristics that might be responsible for its neurotoxicity. Bilirubin interaction with membranes will be studied by small angle x-ray diffraction to seek any role bilirubin might play in modifying general transport and electron transport in membranes. The possible role of bilirubin-nucleic acid interaction in toxicity will be studied by the elucidation of the molecular interaction of bilirubin-oligonucleotide complexes.